Dronedarone (SR33589) is a benzofuran derivative that is a new potent drug in the treatment of arrhythmia. Chemically, dronedarone is similar to amiodarone, but it has no iodine, so it is less lipophilic than amiodarone. Dronedarone not only retains the curative effects of amiodarone, but also has no extracardiac adverse response of amiodarone. It is expected to become a drug that is more safe, tolerated better by patients, and one alternative of amiodarone for the treatment of arrhythmia.
Along with the faster moving social modernization process and the higher social pressure people bear, the number of patients with cardiovascular disease in our country is increasing. Cardiovascular disease is listed as one of the top ten causes of death. Therefore, the development of dronedarone will bring great economic benefit and social benefit. Dronedarone is represented as formula [I]:

U.S. Pat. No. 5,223,510A disclosed a process for preparing dronedarone as shown in scheme 1. In this patent, dronedarone is prepared by converting 2-butyl-5-nitrobenzofuran to 5-amino-2-butyl-3-(4-[3-(dibutylamino)propoxy]benzoyl)benzofuran (compound A) via acylation, hydrolysis, O-alkylation and reduction; then reacting the compound A with methanesulfonyl chloride in the presence of triethylamine as a catalyst to obtain acyl compound; and then purifying the acyl compound by column chromatography. Finally, dronedarone hydrochloride is obtained by treating dronedarone with hydrogen chloride-ether in ethyl acetate.

In this process, the compound A is reacted with methanesulfonyl chloride to easily obtain the undesired double methanesulfonyl compound (a compound of formula Ia), which requires a further purification of dronedarone by column chromatography. It is not very economic for industrial production. In addition, an additional salifying step of dronedarone hydrochloride is needed which costs more reaction equipment and reduces overall yield, and increases production costs at the same time.

Many processes for the acylation of amines have been reported. U.S. Pat. No. 5,223,510A also disclosed that double methanesulfonyl compound IIa, not monomethyl sulfonyl compound (II), is obtained by reacting 5-amino-2-butyl-benzofuran in carbon tetrachloride with methanesulfonyl chloride in the presence of triethylamine as a catalyst. Compound IIa can be converted to compound II via deacylation with an additional deacylation step, which also increases the production cost, and is unfavorable for industrialized production. It is shown in scheme 2:

WO 03/048144A2 reported a process for preparing compound II by adjusting the proportion of compound II and compound IIa under different catalysts to an optimized condition (5<Pka<10) by using 2-butylbenzofuran-5-amine.
Subsequently, US2005049302 described a process for preparing compound II, not compound IIa, from 5-amino-2-butyl-benzofuran. In this process, compound II is reacted with compound III in the presence of tin tetrachloride (scheme 3) to obtain dronedarone with low yield and complicated operations, such as column chromatography etc., which is not suitable for industrial production.

Therefore, it is more beneficial to get a process for preparing dronedarone and salts thereof having simple operation, high yield, low cost, and suitable for industrialized production.